1. Field of the Invention
This invention relates to braking systems for vehicles and more particularly to a braking system which utilizes the braking component of the friction force provided during the use of non-parallel wheels.
2. Description of the Related Art
Hydraulic or pneumatic brakes which are typically used for vehicles can fail because of seal degradation, leakage and/or failure of other components due to the complexity of pressurized brakes. A number of special braking design methods have been proposed for increasing the reliability of braking systems and/or for providing emergency braking systems.
For example, U.S. Pat. No. 2,351,935 issued to L. J. Devlin, entitled "Emergency Braking Device", discloses an emergency braking device for an aircraft in which "toe-out" of the wheels is provided which serves as the source of a braking force. The toe-out is provided by a relatively complex mechanism automatically operable upon release to frictionally engage the tire of an aircraft landing wheel and cause the tire and wheel, by reason of their rotative force to travel in an arc about a substantially vertical wheel support.
The Devlin device requires numerous components, including for example, a steel cable, bell crank, and specially designed notched surfaces. To insure wheel toe-out, a spring-loaded cam rotates into the tire sidewall with the resulting friction force being used to initiate toe-out. (Use of this cam may be unsafe, increasing the chances of tire blowout.) Furthemore, there is not direct coordination of toe-out motion. One wheel could toe-out faster than the other, causing a yaw shock (a right or left steering anomaly).
Inasmuch as the Devlin device is directed to emergency applications, it cannot be modulated. It is either full-on or off. Toe-out occurs almost instantaneously, producing an enormous opening shock, very likely requiring the addition of a load snubber.
Devlin et al's use of toe-out as the only source of the braking force is inefficient because it requires a very large toe-out angle (20.degree.), which may result in tire blowout.
U.S. Pat. No. 2,538,389, entitled "Aircraft Landing Gear", issued to A. C. Smith, discloses an aircraft landing gear which deploys the skid under the wheel to provide friction at the runway/skid interface. The invention is intended for fixed main gear light aircraft and the skid system is used only for emergencies. In normal flight, the entire main gear of the Smith device is positioned for emergency use and must, for a normal landing, be rotated 90 degrees about the main gear struts. At the same time, the skid must also be rotated 90 degrees upward. The main gear complexity required for each normal landing is fraught with safety and reliability concerns as well as probable excessive cost and weight. In view of the above, there is a need for a simple, efficient braking device for use with vehicles utilizing wheels for vehicle motion relative to a surface.